With respect to a circuit board for making up or mounting electronic parts, such as packaged LSIs such as BGA and CSP, MCM, and other integrated circuit devices, it is necessary to inspect the electrical properties of the circuit board before the electronic parts or the like are assembled or mounted for the purpose of confirming that a wiring pattern of the circuit board has the expected performance.
As an inspection apparatus for inspecting the electrical properties of a circuit board, there has heretofore been known that comprising an inspection electrode device, in which a great number of inspection electrodes are arranged, and an adaptor for electrically connecting the inspection electrodes in this inspection electrode device to electrodes to be inspected of a circuit board that is an object of inspection. As the adaptor of such an inspection apparatus, there has been known that having a wiring board for connection called a pitch converting board and composed of a printed wiring board and an anisotropically conductive elastomer sheet arranged on the surface of this wiring board for connection.
As the wiring board for connection in this adaptor, are known that having, on a front surface thereof, a plurality of connecting electrodes arranged in accordance with a pattern corresponding to a pattern of electrodes to be inspected of a circuit board, which is an object of inspection, and, on a back surface thereof, a plurality of terminal electrodes arranged in accordance with a pattern corresponding to a pattern of a plurality of inspection electrodes selected from the great number of the inspection electrodes in the inspection electrode device (see, for example, Patent Art. 1), that having, on a front surface thereof, pairs of connecting electrodes each composed of a connecting electrode for current supply and a connecting electrode for voltage measurement and arranged in accordance with a pattern corresponding to electrodes to be inspected of a circuit board, which is an object of inspection, and, on a back surface thereof, a plurality of terminal electrodes arranged in accordance with a pattern corresponding to a pattern of a plurality of inspection electrodes selected from the great number of the inspection electrodes in the inspection electrode device (see, for example, Patent Art. 2), and the like. The adaptor having the former wiring board for connection is used in, for example, an open short-circuit test of each circuit in a circuit board, and the adaptor having the latter wiring board for connection is used in an electric resistance-measuring test of each circuit in a circuit board.
On the other hand, the anisotropically conductive elastomer sheet is a sheet exhibiting conductivity only in its thickness-wise direction or exhibiting conductivity only in the thickness-wise direction when it is pressurized, and those of various structures have heretofore been known. For example, Patent Art. 3 discloses an anisotropically conductive elastomer sheet (hereinafter also referred to as “dispersion type anisotropically conductive elastomer sheet”) obtained by uniformly dispersing metal particles in an elastomer, and Patent Art. 4 discloses an anisotropically conductive elastomer sheet (hereinafter also referred to as “uneven distribution type anisotropically conductive elastomer sheet”) obtained by unevenly distributing particles of a conductive magnetic substance in an elastomer to form a great number of conductive path-forming parts each extending in a thickness-wise direction thereof and an insulating part mutually insulating them. Further, Patent Art. 5 discloses an uneven distribution type anisotropically conductive elastomer sheet with a difference in level defined between the surface of each conductive path-forming part and an insulating part.
These anisotropically conductive elastomer sheets are obtained by charging a molding material with conductive particles exhibiting magnetism contained in a material for polymeric substance, which will become an elastic polymeric substance by being cured, into a mold, thereby forming a molding material layer having a necessary thickness, applying a magnetic field to the molding material layer in a thickness-wise direction thereof and subjecting the molding material layer to a curing treatment. In such an anisotropically conductive elastomer sheet, the conductive particles are contained in the base material composed of the elastic polymeric substance in a state oriented so as to align in the thickness-wise direction, and a conductive path is formed by a chain of a great number of the conductive particles.
Among such anisotropically conductive elastomer sheets, the dispersion type anisotropically conductive elastomer sheet has the advantage of the following points compared with the uneven distribution type anisotropically conductive elastomer sheet.    (1) The uneven distribution type anisotropically conductive elastomer sheet needs to be produced by using a special and expensive mold, whereas the dispersion type anisotropically conductive elastomer sheet can be produced at low cost without using such a mold.    (2) The uneven distribution type anisotropically conductive elastomer sheet needs to form conductive path-forming parts in accordance with a pattern corresponding to a pattern of electrodes to be inspected and is individually produced according to a circuit board that is an object of inspection, whereas the dispersion type anisotropically conductive elastomer sheet can be used irrespective of the pattern of electrodes to be inspected and thus has general-purpose property.    (3) Since the uneven distribution type anisotropically conductive elastomer sheet exhibits conductivity at its conductive path-forming parts in the thickness-wise direction thereof and does not exhibit conductivity at its insulating part, positioning of the conductive path-forming parts to electrodes to be inspected is required when the uneven distribution type anisotropically conductive elastomer sheet is used, whereas the dispersion type anisotropically conductive elastomer sheet exhibits conductivity over the whole surface thereof in the thickness-wise direction thereof, and so positioning to the electrodes to be inspected is unnecessary, and an electrically connecting operation becomes easy.
On the other hand, in the uneven distribution type anisotropically conductive elastomer sheet, the insulating part mutually insulating adjacent conductive path-forming parts is formed between the adjacent conductive path-forming parts, so that the uneven distribution type anisotropically conductive elastomer sheet has the advantage of having performance that electrical connection to respective electrodes to be inspected can be achieved with high reliability in a state that necessary insulating property has been retained between adjacent electrodes to be inspected even about a circuit board, in which the electrodes to be inspected are arranged at a small pitch, i.e., having high resolving power compared with the dispersion type anisotropically conductive elastomer sheet.
In the dispersion type anisotropically conductive elastomer sheet, however, higher resolving power is achieved as its thickness becomes smaller because conductive paths formed in the thickness-wise direction become short. Accordingly, that having a small thickness is used as the dispersion type anisotropically conductive elastomer sheet in the adaptor when a circuit board, in which a pitch between electrodes to be inspected is small, is inspected.
In an inspection apparatus for circuit board, which is equipped with such an adaptor as described above, a circuit board (hereinafter also referred to as “circuit board to be inspected”), which is an object of inspection, is conveyed in an inspecting region by, for example, a conveying mechanism of the rail-conveying type having a conveyor belt and a guide rail, the anisotropically conductive elastomer sheet in the adaptor is brought into contact with electrodes (hereinafter also referred to as “electrodes to be inspected”) of the circuit board conveyed to the inspecting region, and the anisotropically conductive elastomer sheet is pressurized in the thickness-wise direction thereof, whereby electrical connection of the electrodes to be inspected of the circuit board to be inspected to the inspection electrodes in the inspection electrode device is achieved. In this state, necessary electrical inspection as to the circuit board to be inspected is conducted. After electrical inspection as to one circuit board to be inspected is conducted, the pressurization against the circuit board to be inspected is released, the circuit board to be inspected is conveyed from the inspecting region to a proper place, another circuit board to be inspected is conveyed to the inspecting region, and the same operation as described above is repeated on said another circuit board to be inspected, thereby conducting electrical inspection (see, for example, Patent Art. 6).
However, the adaptor used in such an inspection apparatus for circuit boards involves the following problems.
More specifically, the elastic polymeric substance, for example, silicone rubber, forming the anisotropically conductive elastomer sheet bears adhesive property by pressurization, so that the anisotropically conductive elastomer sheet may adhere to the surface of the circuit board to be inspected in some cases when the pressurization against the circuit board to be inspected is released, and may not be easily separated from the circuit board to be inspected. When such a phenomenon takes place, the circuit board to be inspected, which has completed the inspection, is not surely conveyed from the inspecting region, or the anisotropically conductive elastomer sheet is separated from the wiring board for connection as it adheres to the circuit board to be inspected, and the circuit board to be inspected is conveyed in this state. As a result, the electrical inspection of a subsequent circuit board to be inspected cannot be carried out. As described above, the conventional adaptor involves a problem that it is difficult to smoothly conduct an inspection operation when the electrical inspection is continuously conducted on a great number of circuit boards to be inspected.
As means for solving such a problem, are considered a means that the anisotropically conductive elastomer sheet is fixed to the wiring board for connection by means of a fixing tool, a means that the anisotropically conductive elastomer sheet is fixed to the wiring board for connection with an adhesive, and the like.
However, the former means involves a problem that since the elastic polymeric substance forming the anisotropically conductive elastomer sheet is flexible and low in strength, a portion of the anisotropically conductive elastomer sheet, which has been fixed by the fixing tool, is easy to be broken, and particularly, the portion is early broken when the thickness of the anisotropically conductive elastomer sheet is small. As a result, the service life of the anisotropically conductive elastomer sheet is short.
On the other hand, the latter means involves a problem that it is difficult to replace only the anisotropically conductive elastomer sheet by a new one when the anisotropically conductive elastomer sheet suffers from trouble, and so it is necessary to replace the whole adaptor including the wiring board for connection. As a result, increase in inspection cost for circuit boards is incurred.
Further, as means for inhibiting the adhesion of the anisotropically conductive elastomer sheet to the circuit board to be inspected, have been proposed a means that an adhesion-preventing film is provided on the surface of the anisotropically conductive elastomer sheet (see, for example, Patent Art. 7), a means that the surface of the anisotropically conductive elastomer sheet is subjected to an anti-adhesion treatment such as a corona discharge treatment, glow discharge treatment, plasma treatment, flame treatment, ozone treatment, electromagnetic wave treatment or radiation treatment (see, for example, Patent Art. 8), and a means that the surface of the anisotropically conductive elastomer sheet is roughened (see, for example, Patent Art. 9).
However, these means make it possible to inhibit the adhesion of the anisotropically conductive elastomer sheet to the circuit board to be inspected, but it is difficult to prevent the anisotropically conductive elastomer sheet from separating from the wiring board for connection. After all, it is necessary to fix the anisotropically conductive elastomer sheet to the wiring board for connection by means of the fixing tool or adhesive.    Patent Art. 1: Japanese Patent Application Laid-Open. No. 249924/1994;    Patent Art. 2: Japanese Patent Application Laid-Open No. 2001-235492;    Patent Art. 3: Japanese Patent Application Laid-Open No. 93393/1976;    Patent Art. 4: Japanese Patent Application Laid-Open No. 147772/1978;    Patent Art. 5: Japanese Patent Application Laid-Open No. 250906/1986;    Patent Art. 6: Japanese Patent Application Laid-Open No. 258350/1995;    Patent Art. 7: Japanese Patent Application Laid-Open No. 2001-185260;    Patent Art. 8: Japanese Patent Application Laid-Open No. 2001-185258;    Patent Art. 9: Japanese Patent Application Laid-Open No. 2003-77560.